Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Chimney Lining - Single Vs Double Wall

Question about chimney lining.... The project is a combination category I furnace and natural draft WH currently venting into a masonry chimney with 7 x 7 clay flue tiles. I'll be putting in a 5" (appropriate for BTU) liner and am deciding between single wall and type b venting. There's obviously a cost premium for the type b.

The chimney is an "exterior" chimney for code purposes. Any thoughts on using type B over single wall vent material? The home is located in WI and I was thinking the type B might offer some insulation advantages over the single wall. Any thoughts?

The liner needs to "approved" for the purpose, but if the "dead air space is created by another sheet metal pipe OR your existing clay liner, I don't see a difference in outcomes.

The main issues are the amount of heat it takes to warm up the clay so it can actually do it's job and VENT and the larger size is not conducive to quickly warming up and Venting, so you are also reducing the size as per code. The min BTU size thing was not always on the books and understood til about 10 years ago, maybe a little longer, it's a little fuzzy

You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

Air space in b-vent keeps temperature of fue gas better less heatt absorbed by clay liner. If moisture gets into liner or worse the bricks of the chimmeny it will freeze and pop. Have seen this many times with a 4" liner in a 8 by 8 liner. Had to pull liner and insulate with "approved" sleeve. Fixes it every time.

The only product I know about is vermiculate and well we all know about that now... I agree that a single wall will do he job, I just think under certain conditions a b vent is a better option for the house.